1. Field of the Invention
The present invention relates to a hydrophilic member which has an amphiphilic surface, that is, a surface having both hydrophilicity and hydrophobicity, and can permanently maintain this nature.
2. Background Art
A part of the present inventors has previously proposed a method for highly hydrophilifying the surface of articles by photoexcitation of a semiconductor photocatalyst (WO 96/29375 and WO 97/23572). According to this method, the surface of articles can be highly hydrophilified to a contact angle of the surface with water up to about 0xc2x0.
When this method is applied to, for example, transparent articles such as windshields for vehicles, door mirrors, windowpanes for buildings, eyeglass lenses, or mirrors, the surface thereof is highly hydrophilified, preventing the surface of the articles from being fogged by moisture condensate or steam or from being blurred by water droplets adhering on the surface thereof. Further, when the method is applied to buildings or articles which are disposed outdoors, oil repellent or hydrophobic dust and contaminants adhering on the hydrophilified surface are easily washed away by raindrops, thus permitting the surface to be cleaned.
The present inventors have clarified the state of the surface hydrophilified by the application of the method described in WO 96/29375 and WO 97/23572 and found that the hydrophilic surface has hydrophobic nature as well and that the properties of the hydrophilified surface can be further improved. The present invention has been made based on such finding.
Accordingly, an object of the present invention is to provide a hydrophilic member which has an amphiphilic (hydrophilic and hydrophobic) surface and can permanently maintain this property.
Another object of the present invention is to provide a process for producing a member having an amphiphilic surface and a method for amphiphilifying (hydrophilifying and hydrophobifying) the surface of a member.
The hydrophilic member according to one aspect of the present invention comprises a substrate and a layer, containing a photocatalyst, provided on the substrate. The surface of the layer containing a photocatalyst has a hydroxyl group fixed thereon upon photoexcitation of the photocatalyst. Furthermore, the surface of the layer containing a photocatalyst has a water molecule physically adsorbed in the vicinity of the hydroxyl group upon photoexcitation of the photocatalyst.
The hydrophilic member according to another aspect of the present invention comprises: a substrate; and a layer, containing a photocatalyst, provided on the substrate, the photocatalyst comprising a metal oxide, only oxygen atoms at bridging sites in the metal oxide being substantially exposed on the surface of the layer.
The process for producing a member having an amphiphilic surface according to the present invention comprises the steps of: providing a substrate; and forming a layer containing a photocatalyst on the substrate.
The method for amphiphilifying the surface of a member according to the present invention comprises the steps of: providing a substrate; forming a layer containing a photocatalyst on the substrate; and photoexciting the photocatalyst to amphiphilify the surface of the layer.